MXPA98009796A - Term switch - Google Patents

Abstract

A thermal switch assembly including a dielectric separator and a shape memory metal sheet member sandwiched between a pair of flat metal plates is described, the spacer provides a cavity between the plates, and the sheet member The commutator has a switch blade portion projecting into the cavity, the switch blade member having a mounting portion that engages one of the metal plates, and the switch blade portion is normally under flexural stress. in engagement with the other metal plate to provide a current path between the plates, at elevated temperatures, the shape memory metal switch sheet portion moves out of engagement with the other metal plate to interrupt the path of current; integral fasteners with the dielectric separator cooperate with the metal plates and the switch blade member to keep the assembly from mutator together with the separator and mounting portion of the switch sheet member sandwiched compressively between the metal plates

Description

THERMAL SWITCH BACKGROUND OF THE INVENTION This application relates to the technique of the switches »and more particularly to thermal switches that move automatically from one position to another in response to a high temperature. The invention is particularly applicable for a normally closed switch that moves to an open position to avoid thermal runaway in batteries and will be described with specific reference thereto. However, it will be appreciated that the invention has broader aspects and that it can be used in normally open switches as well as for other purposes. Overcharging batteries of certain types can cause thermal runaway that raises the internal temperature of the battery. The internal pressure within the sealed battery case increases with increasing temperature and an explosion may occur when the internal pressure exceeds the explosion resistance of the battery case. The explosion of a battery releases byproducts that are caustic, toxic, and flammable, and the force of the explosion can cause injury to people or property damage. Thermal protectors of various types have been proposed and used in batteries to interrupt the battery circuit when a predetermined temperature is exceeded. The space available for rechargeable small rechargeable batteries in modern electronic devices such as cell phones requires miniature temperature protection devices. Miniaturization is limited in thermal protectors that use bimetals or thermistors that have a coefficient of resistance to positive temperature because these devices do not work properly or reliably if they become too small. Provisions have been proposed for incorporating a shape memory alloy thermal switch activator into the physical structure of a battery internally of the battery case. Such arrangements can not be used with existing battery designs and it would be desirable to have an integral thermal switch assembly with a memory alloy current carrying activator that could be used for a variety of purposes including externally attached to a battery case .

BRIEF DESCRIPTION OF THE INVENTION A normally closed miniature thermal switch has a memory metal current carrying switch leaf activator that automatically moves to an open position in response to a high temperature or an overcurrent condition. The commutator sheet is on a commutator sheet member which is sandwiched with a dielectric separator between a pair of substantially flat metal plates, the commutator sheet projecting into a cavity between the plates which is formed by an opening in the separator. A mounting portion of the switch blade member engages one of the plates "and the outer end of the switch blade engages the other plate. The switch blade responds at a high temperature to move its outer end away from the other plate and open the circuit. The switch blade preferably remains in its open position after cooling so it operates with a one-step fuse that can not be reset. In a preferred arrangement, the entire outer surfaces of the metal parts of the commutator assembly are coated with a precious metal. The precious metal coating is preferably on the outer peripheral surfaces of the metal parts as well as on the opposite surfaces thereof. The complete switch assembly can be encapsulated or wrapped in electrical insulating material with electrical terminals on the switch assembly projecting through the insulating material. The leaf activator of the current carrying shape memory metal has an outer end that couples an inner surface of a metal plate with contact substantially in line in the closed position of the commutator. The thermal switch according to the present invention preferably has a strength that is less than 20 milliohms, very preferably less than 10 milliohms, and more preferably no more than about 5 milliohms. In a preferred arrangement, the one-piece dielectric separator has integral clamping projections which cooperate with the metal plates to hold the switch assembly together. In one arrangement, the clamping projections on the dielectric separator extend through holes in the metal plates and are deformed on the opposite sides of the metal plates of the separator to complete the assembly. According to another aspect of the invention, the dielectric separator has at least one end portion of reduced thickness defining at least one notch in which a mounting portion of the commutator blade member is received. The depth of the notch is preferably no greater than the thickness of the mounting portion of the switch blade member and most preferably is slightly less than the thickness thereof. This ensures an adequate compressive coupling between the mounting pressure of the switch blade member and the inner surface of a metal plate. The switch blade member preferably has a thickness that is not greater than the thickness of the spacer and the spacer has a thickness that is no greater than about 1.27 mm. In a preferred arrangement, the current-carrying commutator leaf activator in its deformed martensitic state is under less than about% bending stress, and most preferably not more than about 4%. The current carrying switch leaf activator is tensioned by bending between the metal plates to ensure adequate contact and provide low resistivity. The metal plate of the switch assembly that engages the mounting portion of the switch blade member is fixed to a battery terminal or to a battery case externally of the battery case. Heat is conducted from the battery case or battery terminal to the commutator sheet member through the metal plate. Although the switch blade member can be designed to have many different operating temperatures, it can be designed to open at any temperature up to about 125 ° C when used with conventional small rechargeable batteries and very preferably at a temperature on the scale of 65-75 ° C. A principal object of the present invention is to provide an improved thermal switch assembly.

Another object of the invention is to provide an integral thermal switch assembly that uses a shape memory alloy current carrier switch blade activator. A further object of the invention is to provide a thermal switch assembly that can be externally fixed from a battery to protect the battery against thermal runaway. A further object of the invention is to provide a miniature thermal switch assembly having a shape memory metal current carrying switch sheet activator and which is relatively simple and inexpensive to manufacture and assemble. It is also an object of the invention to provide a current limiting switch assembly having a shape memory metal current carrying activator.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side elevational view of a thermal switch constructed in accordance with the present invention; Figure 2 is a top plan view thereof; Figure 3 is a side elevation view of a dielectric separator used in the thermal switch assembly of Figures 1 and 2; Figure 4 is a bottom plan view thereof; Figure 5 is a side elevational view of a switch blade member; Figure 6 is a top plan view thereof; Figure 7 is a side elevation view of a metal plate used in the switch assembly of Figures 1 and 2; Figure 8 is a top plan view thereof; Figure 9 is an exploded perspective illustration of the switch assembly of Figures 1 and 2 together with a cover of a battery housing on which the battery assembly is mountable; Figure 10 is an enlarged perspective illustration of a dielectric separator »showing how a mounting portion of a switch blade member is received in a notch in the separator; Figure 11 is a side elevational view showing the switch assembly mounted on top of a battery case having a negative terminal and a positive case; Figure 12 is a side elevation view of a battery »showing the switch assembly mounted on the bottom of a battery case that has a positive terminal and a negative case; Figure 13 is a side elevational view of a switch blade member; Figure 14 is a side elevational view of the switch blade member under bending tension between a pair of metal plates; Figure 15 is an elongated side elevation view of an end portion of a switch blade; Figure 16 is an elongated side elevation view of a modified end portion of a switch blade; Figure 17 is a side elevational view of another embodiment; Figure IB is a view in extreme elevation thereof; Figure 19 is a top plan view thereof; * Figure 20 is a side elevational view of a spacer used in the embodiment of Figures 17-19; Figure 21 is a view in extreme elevation thereof; Figure 22 is a top plan view thereof; Figure 23 is a side elevational view of a shape memory alloy current carrying switch activator and contact blade used in the embodiment of Figures 17-19; Figure 24 is a top plan view thereof; Figure 25 is a side elevational view of a plate used in the embodiment of Figures 17-19 and Figure 26 is a top plan view thereof.

DESCRIPTION OF A PREFERRED MODALITY Referring now to the drawings »in which what is shown is for reasons of illustrating a preferred embodiment of the invention only and not for reasons of limiting it» Figures 1 and 2 show a switch assembly A having a member of sheet metal shape memory switch 10 and a separator dielectric 12 sandwiched between a pair of substantially flat rectangular metal plates 14 »16. A nickel thin-film terminal 18 is welded to an outer surface of the plate 14 adjacent one end of the switch assembly A and projects outwardly from the same to connect the switch assembly A in an electrical circuit. Another thin nickel terminal 20 is welded to an outer surface of the plate 16 adjacent to the end of the switch assembly A »opposite the terminal IO 18 and projecting out of it for the connection in an electrical circuit. The separator 12 is molded into a piece of plastic material and has a substantially rectangular opening 22 therein to provide a cavity 24 between the metal plates 14"16. The switch blade member 10 has a portion of switch sheet elongated 30 < It extends into the cavity 24 and is normally bent or curved upwardly as shown in Figure 1 with an edge at the end 32 engaging an inner surface of the plate 14 with in-line contact to complete an electrical circuit between the plates 14, 16. The switch blade member 10 is a shape memory metal and responds to an elevated temperature by automatically moving away from the plate 14 back to a substantially flat position to open the circuit between the plates 14 and 16. The switch blade portion 30 also defines a shape memory metal commutator and current carrying contact activator. With reference to Figures 3 and 4 »the separator 12 has opposite end areas 36» 3B with integral holding projections 40 »42 and 44» 46 extending outwardly thereof in opposite directions. Each clamping projection 40-46 is a substantial cylindrical protrusion located centrally on end areas 36"38 and extending outwardly thereof at a distance slightly greater than the thickness of each metal plate 14" 16.

Aline separator 50 »52 connect the end areas 36» 38 to define the boundaries of a rectangular separator opening 22. A surface of the end area 36 on the separator 12 has notches as indicated by number 54 in Figures 3 and 4 »So that the end area 36 of the separator has a reduced thickness. With reference to Figures 5 and 6 »the switch blade member 10 is shown substantially T-shaped with a substantially rectangular mounting portion 60 having an elongated commutator blade portion 30 extending outwardly therefrom. A centrally located circular hole 62 is provided in the mounting portion 60. The length of the switch blade activator portion 30 is preferably less than 12.7 mm, most preferably less than 10, and more preferably less than about 7.62 mm. Figures 7 and B show a substantial substantially flat metal plate 14 having a circular hole 66 '6B adjacent to the opposite ends thereof. It will be recognized that the substantially rectangular and substantially flat metal plate 16 has the same structure as the plate 14 shown in Figures 7 and B. The circular holes of the plate 16 are identified by the numbers 70 »72 in Figure 9. With Referring to Figure 9, the switch is assembled by placing the mounting portion 60 of the switch blade member 10 within the notch 54 of the spacer 12 and with the holding projection 42 extending through the hole 62. Separator projections 42. 46 extend through holes 70 »72 in plate 16. Opposite separator projections 40» 44 that are not shown in Figure 9 are extended through holes 66 »6B in plate 14. The complete assembly is after held in compression while the separator projections 40-46 are deformed outwardly by ultrasonic or thermal energy to a larger diameter than the holes 66-72 to complete the assembly. The mounting portion 60 of the switch blade member 10 is under compression in engagement with the inner surface of the plate 16 for proper contact. Figures 11 and 12 are open views of a typical battery B having a case C including an upper part or cover 80 having a depression therein and a bottom 82. An electrode assembly D placed inside the battery case C it has an electrode connected to the battery case C by means of the wire 90 and its other electrode connected by means of a wire 94 to the battery terminal 92 extending through the battery cover 80. In Figure 11 »the wires 90 and 94 are connected to the positive and negative electrodes so that the battery terminal 92 is negative and the battery case C is positive. Figure 12 has the inverse arrangement with the wires 90 and 94 connected respectively for the battery terminal 92 to be positive and the battery case C to be negative. The battery case C can be made of metal or a plastic that is electrically conductive or can be coated with an electrically conductive metal. The electrode assembly D can be of any type including "plate and spiral winding stack" and is generally shown as a spiral wound type. In said structure the strips of anode and cathode material with a separating strip between them are wound in a shape for reception in the open upper containing portion of the battery case having integral peripheral and lower walls. The anode material is a consumable metal and the cathode material is reducible by electrochemical action. The separator is a porous electrical insulating material that is ionically conductive. The electrode assembly is inserted into the container forming the battery case and a solvent electrolyte containing a conductive solute is added to the container. The cover is then fixed in a sealable manner to the open top portion of the container portion to seal the electrode and electrolyte assembly within the battery case. Fig. 11 shows the switch assembly A received within the depression in the battery cover 80 »and with the nickel thin sheet electrode 20 welded to the battery terminal 92. In Fig. 12» a thin sheet terminal of flat nickel 20a extends outwardly from the metal plate 16 instead of the angled terminal 20 and is welded to the bottom 82 of the battery case C. The complete switch assembly "except for the terminals" is preferably either encased or wrapped in a electrical insulating material. The plastic material can be molded onto the switch assembly; Shrink wrapping material or wrapping tape can be used. The switch blade member 10 is preferably of a nickel-titanium shape memory alloy. However, it will be appreciated that other shape memory alloys may be used such as copper-based ternary alloys including copper-zinc-aluminum and copper-nickel-aluminum. The scale of temperatures of transition to. which the alloy changes from its deformed configuration to its recovered configuration can also vary significantly by selecting different shape memory alloy compositions and varying the heat treatment methods. The switch blade member 10 is stamped and cut to its flat configuration shown in Figs. 5 and 6 'and then heated to its aetheritic transformation temperature followed by cooling to its martensitic temperature. The switch blade portion 30 is then bent to a permanently deformed position relative to the mounting portion 60 as shown in FIG. 13. With the switch blade portion 30 deformed as shown in FIG. under approximately 4M of voltage determined by the formula e = l / E2R / t) + 13 »where e is the percentage stress» R is the radius of curvature for the commutator sheet portion 30 as shown in figure 13 » and t is the thickness of the switch blade portion 30. The amount of flexural stress is preferably less than about 8% and most preferably less than about 4%. It will be recognized that this is an approximation for the amount of tension that is in the switch leaf portion 30. The limit on the percentage stress is desirable so that the switch does not close again once opened Although the switch blade member can be heat treated and deformed to return to its closed position after cooling, it is preferred according to the present invention to have a switch blade member that remains open even after cooling. In this manner »when the switch blade moves from a closed position to an open position in response to a high temperature condition. it remains open even after the high temperature condition no longer exists. If the commutator blade portion is deformed beyond the indicated percentage stress, it will cause permanent relaxation of the metal beyond the elastic limit which may cause it to return to its closed position after cooling. In this way, it is possible to obtain a switch that can be closed again after cooling if desired by initially doubling the switch blade activator to more than about 8% voltage. The dielectric separator 12 is preferably of a relatively hard material having a high tensile strength »low water absorption and high heat deflection temperature. The material preferably has a tensile strength of at least 1 »054.5 kg / cm53» and most preferably at least 1,406 Kg / cm52. The heat deflection temperature at 18.56 kg / sm53 is preferably at least 260 ° C. The water absorption after 24 hours at 22.7 ° C is preferably no greater than about 0.02%. The dielectric separator 12 can be made of many different materials having these desirable properties and one example is glass filled polyphenylene sulfide. A suitable material is available from General Electric Company under the name SupecG410T. Other suitable material is available from RTP Co. under the name RTP1300 series P-1. Another material available from General Electric Co pany is Valox EF4530 PBTP resin. All these materials are reinforced with glass and other materials that have these desirable properties are also available. The vertical extension of the switch blade end 30 in a deformed martensitic state is indicated by the number 90 in Fig. 13. This vertical height is reduced when the switch blade member is sandwiched between the metal plates 14"16. To ensure adequate contact between the inner surface of the plate 14 and the end of the switch blade portion 30 »the vertical height 90 is preferably reduced by at least 15%» very preferably at least 2G% and more preferably at least 25% Although larger reductions in this vertical distance are possible »the maximum is preferably not greater than about 40% or one such that causes the metal to relax. Figure 14 shows the portion of switch sheet 30 under tension by bending between the plates 14 »16 with a reduced vertical height 90a. As an example »if the height 90 measures approximately 45-55 thousandths of 25.4 mm >; the height 90a is approximately 8-12 thousandths of 25.4 m smaller. Figure 15 shows the end 32 of the switch blade portion 30 with a relatively sharp edge at the intersection of the upper surface of the sheet portion with the leaf end. This edge makes a generally linear contact with the inner surface of the metal plate 14 in the closed position of the switch. Figure 16 shows a rounded end 32a which will still make an essentially linear contact with the inner surface of the plate 14. Although many other extreme shapes can be provided, these will essentially make linear contact with the inner surface of the metal plate. The coupling line is between precious metal coatings on the plate and the inner surface of the plate.

With reference to Figures 12 and 11 »the switch assembly A is fixed to the battery terminal or to the battery case so that the heat is conducted to the outer metal plate 16 which directly couples the mounting portion 60 of the member of switch sheet 10 for adequate heat transfer. The heat is conducted from the battery case or terminal to the metal plate 16 and up to the switch blade member IO. The temperature of the switch sheet member 10 is also raised by I3R clamping and can be constructed to operate at many different elevated temperatures. By way of example, the switch blade portion can be moved from its closed position to an open position at a temperature of about 65-75 ° C. The switch can be constructed to open at an elevated temperature on the 60-125 ° scale. The heat that causes the switch to open can come from heating by I R »by conduction from the case and the terminal of the battery» by convection from the environment in which the switch is installed »or from a combination of these. The reference to a thermal switch encompasses switches that respond to any one or more of these heat sources. In the present invention, the shape memory metal current and contact activator defined by the switch leaf portion 30 is in its martensitic deformed configuration in the closed position of the switch. At the high operating temperature the commutator blade portion assumes its recoverable anthustic shape and moves to an open switch position. After the rotation »the commutator blade portion does not move back to its closed position so the commutator assembly functions as a one-pass fuse. This is mainly achieved by controlling the percentage voltage in the current carrying switch leaf activator in its deformed configuration. Although the shape memory metal can be processed so that the switch is reclosed after cooling and the present invention covers said arrangements, the most preferred arrangement is one in which the actuator does not return completely to its deformed configuration. his state recovered after cooling. All metal parts of the commutator assembly "other than the nickel electrodes" are preferably plated with a precious material such as silver, gold, platinum or palladium to provide adequate electrical conductivity. The plating is provided on both opposing surfaces of the metal plates and the switch blade member as well as on the outer peripheral surfaces thereof. It will be recognized that the precious metal coating can be applied in forms that are different from electroplating, such as by vacuum deposition or sputtering. Although it is preferred to coat the entire outer surfaces of the metal parts with a metal JO precious "it will be understood that localized coating of small areas may be possible for some applications. The coating is done before the electrodes 18-20 are fixed. The metal plates 14"16 are preferably made of brass or copper for adequate electrical conductivity and to minimize corrosion in the event that the precious metal coating is scratched or otherwise broken. Although steel plates can be used for some purposes, it is preferred to use metals that have corrosion properties similar to those of brass. Without the nickel terminals 18 and 20 »a prototype switch assembly had a resistivity of less than about 5 milliohms. With the nickel terminals, the commutator assembly had a resistivity of approximately 8-12 milliohms. According to the present invention, the commutator assembly preferably has a resistivity of less than 20 milliohms, most preferably less than about 12 milliohms and more preferably no greater than about 5 or 6 milliohms. With the nickel terminals, the resistivity is preferably less than 20 milliohms and most preferably less than about 12 milliohms. Extremely low resistivity is achieved by a combination of features including the coating of all metal surfaces with a precious metal, the switch assembly under sufficient compression to ensure proper coupling between the mounting portion of the sheet member switch and the inner surface of a metal plate »and providing a switch blade activator with sufficient stiffness and placing it under sufficient tension by bending to ensure adequate contact between the outer end of the sheet and the inner surface of the plate Exterior. The diameter of the clamping projections on the spacer and the diameter of the holes receiving the projections are sized to provide a snap fit. When the term "approximately" is used in this application, it is intended to say more or less 10% unless otherwise indicated or otherwise understood from the context in which it was used. The improved switch assembly of the present invention makes possible iniaturization, and examples of dimensions will be given simply by way of illustration. The metal plates 14"16 each have a thickness of about 0.25" a length of about 13.59 mm and a width of about 5.26 mm. The switch blade member 10 has a thickness of about 0.25 and a full length in its flat condition of about 9.52 mm "a width of the mounting portion of approximately 5.23 mm and a length of the switch blade portion. of approximately 6.35 mm. The spacer 12 has a thickness of approximately 0.635 mm, a length of approximately 13.59 mm and a width of approximately 5.23 mm. The rectangular opening in the separator has a length of approximately 7.24 mm and a width of approximately 3.96 m. The notch 54 has a depth of about 0.25 mm and the full thickness between the opposite ends of the projections 40 »42 and 44» 46 is about 1.40 mm. With the mounting portion of the commutator blade member received in the notch of the separator, the complete external thickness of the commutator assembly between the outwardly facing surfaces of the plates 14"16" is approximately 1.14 mm. The depth of the notch 54 in the separator 12 is preferably no greater than the thickness of the switch blade member 10"and is preferably slightly smaller to ensure adequate compressive contact between the inner surface of the plate 16 and the mounting portion 60. of the switch blade member 10. The material of the separator is more compressible than the metal switch blade member. Therefore, even when the notch has approximately the same depth as the thickness of the switch blade member, there is adequate contact between the mounting portion and the plate 16 due to the high compressive force applied to the assembly while the clamping projections are of ormadas. Figures 17-19 show another embodiment of a switch assembly G having substantially flat upper and lower metal plates 114 and 116. Each plate 114 and 116 has a central projection 115 and 117 extending outwardly from one end of the plate. same to define terminals to connect the switch assembly in a circuit. Figures 20-22 show a substantially rectangular spacer H having opposite end portions 118 and 120 of reduced thickness. Separator side rails 122 and 124 extend the full length of spacer H and are thicker than end portions 118"120. Spacer H has a central rectangular aperture 126 limited by end portions 118., 120 and side rails 122 »124. As shown in Figure 21» the end portion 120 has a thickness that is substantially less than the thickness of the side rails 122 »124 and is substantially centered between the upper and lower surfaces of the rails for defining upper and lower notches in each end portion of the separator H. Each notch is located between side rails 122, 124 on opposite sides of the end portions 118"120. Thus, the separator H is substantially symmetrical and can be used. in any of two inverted positions or two positions from end to end. Non-circular clamping projections 131-133 are located centrally on opposite sides of the end portions 118 and 120. In the arrangement shown, the non-circular projections are substantially square in cross section. The clamping portions are also rotated about 45 ° so that the sides of the square projections extend at about 45 ° toward the side rails 122 »124. The clamping portions can also be considered substantially diamond-shaped and other shapes can be provided that do not. be circular. Each of the four notches in the opposite end portions of the separator H has a depth that is slightly less than the mounting portion of a switch blade member that will be received therein. For example, when a switch blade member has a thickness of approximately 0.25 mm, each notch will have a depth of approximately 0.179 m. Figures 23 and 24 show a rectangular shape sheet alloy switch member I of shape memory. A current carrying switch blade activator and a contact portion 142 extend outward from the mounting portion 140 and terminate at a lower end 144.

A rectangular or diamond-shaped hole 146 is centrally located in the mounting portion 140 and is rotated so that its sides extend substantially 45 ° toward the side edges of the rectangular switch blade member I. The fastener projections 130 and 133 and opening 146 are sized for a snap fit. The width of the switch blade member I is slightly less than the width of a notch between the side rails 122 »124 of the separator H. By way of example» with a switch blade member having a width of approximately 2.36 mm » the width of a notch is approximately 3.2 mm. This ensures that the switch blade portion does not hang on the side rails during the movement of the same »and allows tolerances in the assembly. The non-circular shape of the projections and the corresponding shape of the hole in the commutator blade member provide for an adequate automatic orientation of the commutator blade member during assembly. Figures 25 and 26 show a substantially flat and rectangular metal plate 114 with a centrally located intergral terminal 115 extending outwardly from one end thereof. Square or diamond-shaped holes 150 and 151 are located centrally on the longitudinal center line of the plate 114 adjacent the opposite ends thereof. The holes 150 and 151 are rotated approximately 45 ° so that their sides extend approximately 45 ° towards the sides of the plate 114. The holes 150 and 151 are spaced at the same distance from two clamping projections such as 130 and 132 on the separator H. The holes 150 and 151 are also dimensioned to closely receive clamping projections 130-133 having a length sufficient to extend externally of the plates for deformation thereof by heat or ultrasonic energy to secure the parts assembled under compression.

The arrangement shown and shown with respect to Figures 17-26 facilitates fabrication and assembly because the H separator does not require orientation. Both the upper and lower plate are the same and the switch blade member is mountable in any of the four notches of the separator. Although the switch assembly has been shown and described with respect to a normally closed arrangement, it will be recognized that normally open switches can be constructed using features of the present invention. The switch assembly can be used in other temperature monitoring applications to open a circuit or to close a circuit and sound an alarm. For example, a normally open switch arrangement could be used in fire alarms and would move to a closed switch position in response to a high temperature to sound an audible signal. Although the invention has been shown and described with respect to a preferred embodiment, it is obvious that alterations and modifications equivalent to other experts in the art may occur after reading and understanding this description. The present invention includes all such alterations and equivalent modifications and is limited only by the scope of the claims.

Claims (31)

NOVELTY OF THE INVENTION CLAIMS

1. - A thermal switch comprising a dielectric separator sandwiched between a pair of substantially flat metal plates to define a cavity between said plates - a switch blade member having a mounting portion sandwiched between said dielectric separator and one of said plates metal "said commutator blade member has a switch blade portion extending within said cavity» said blade portion d commutator is of a shape memory metal and has a normally closed position in engagement with the other of said metal plates for providing a current path between said metal plates, and said portion of shape memory metal switch sheet responds to an elevated temperature by moving to an open position out of engagement with the other, said plates of metal to interrupt the current path between said metal plates.

2. The switch according to claim 1, further characterized in that said switch sheet portion remains in said open position after cooling substantially below said elevated temperature.

3.- The switch in accordance with the? B claim 1 further characterized in that said metal plates have interior surfaces facing said cavity and "the switch blade member has opposite surfaces" and at least said inner surfaces of said metal plates and said opposing surfaces of said member; Switch blade are coated with a precious metal.

4. The switch according to claim 3 »further characterized in that said switch blade member has a peripheral surface that is coated with a precious metal.

5. The switch according to claim 1 »further characterized in that said switch is encapsulated in an electrical insulating material and further includes an electrical terminal fixed to each of said metal plates and projecting externally of said electrical insulating material.

6. The switch according to claim 1 »further characterized in that said switch blade portion has a terminal end that couples said other metal plate with substantially linear contact in said closed position thereof.

7. The switch according to claim 1 »further characterized in that said switch has a resistance of less than 20 milliohms.

8. The switch according to claim 1 which includes fasteners integral with said dielectric separator and which cooperate with said metal plates to hold said metal plates together with said separator and said mounting portion of said switch blade member. sandwiches compressively between them.

9. The switch according to claim 8, further characterized in that said fasteners comprise a plurality of clamping projections on said dielectric separator extending towards said metal plates »said metal plates have openings therein receiving said projections, and said clamping projections being deformed on the opposite ends of said metal plates of said spacer.

10. The switch according to claim 9 »further characterized in that said fastening portions have non-circular transverse shapes and said openings have a similar shape.

11. The switch according to claim 8, further characterized in that said metal plates have opposite ends "and said fasteners are located adjacent said opposite ends.

12. The switch according to claim 1, further characterized in that said dielectric separator has a surrounding continuous peripheral portion. said cavity.

13.- The switch of according to claim 1 further characterized in that said dielectric separator has at least one end portion of reduced thickness defining at least one notch in which said mounting portion of said commutator blade member is received.

14. The switch according to claim 12 »further characterized in that said notch has a depth that is not greater than the thickness of said end assembly portion of said switch blade member.

15. The switch according to claim 1 »further characterized in that said separator has opposite end portions of reduced thickness that define four notches, and said mounting portion of said switch blade member is received in one of said notches.

16. The switch according to claim 1 further characterized in that said switch blade member has a thickness that is not greater than the thickness of said separator.

17. The switch according to claim 1 »further characterized in that said separator has a thickness that is not greater than about 1.27 mm.

18. The switch according to claim 1 »further characterized in that said metal plates and said separator are substantially rectangular and said separator has a substantially rectangular separator opening therein to define said cavity.

19. The switch according to claim 18 »further characterized in that said rectangular spacer opening has a width substantially greater than half the width of said spacer and a length that is not less than half the length of said spacer and not greater than three-fourths of the length of said spacer to provide opposing end areas of spacer connected by spacer webs.

20. The switch according to claim 18 »further characterized in that said spacer has spacer end areas at opposite ends of said spacer opening, said spacer end areas having integral fastening projections extending outward from opposite sides of the spacer. same towards said metal plates »said clamping projections have a length greater than the thickness of said metal plates, said metal plates have holes receiving said clamping projections» and said clamping projections are deformed and elongated on the opposite sides of said plates metal of said separator.

21. The switch according to claim 1, further characterized in that said metal plates have exterior surfaces and said switch has a thickness through said outer surfaces that is not greater than about 1.14 mm.

22. The switch according to claim 1, further characterized in that said switch blade member is substantially T-shaped.

23. The switch according to claim 1 »further characterized in that said metal plates have end portions. opposite and at least one of said end portions on at least one of said metal plates has a terminal member fixed thereto.

24. The switch according to claim 1, further characterized in that said switch blade portion has a curved configuration and is less than about 8% flexural stress.

25. The switch according to claim 1 »further characterized in that said separator has a tensile strength of at least 1" OS4.5 kg / cm53.

26. The switch according to claim 1 »further characterized in that said separator has a heat deflection temperature at 18.59 kg / cm3 of at least 260 ° C.

27.- The switch according to claim 1, including a battery having a battery case and a battery terminal »one of said metal plates is fixed to one of said battery case and battery terminal.

28. - The switch according to claim 27, further characterized in that said battery case has a cavity therein and said switch is received in said cavity.

29. In a battery having a battery case and a battery terminal, a thermal switch assembly fixed to one of said battery case and battery terminal externally of said battery case. Said switch assembly includes a dielectric separator. sandwiched between a pair of metal plates and defining a cavity therebetween »a shape memory metal switch blade member has a mounting portion sandwiched between one of said metal plates and said spacer, said sheet metal member The commutator has a portion of commutator blade that extends into said cavity and that is under tension by bending in 'engagement with the other of said metal plates' said portion of commutator blade being moveable out of engagement with said other of said metal plates in response to a high temperature.

30. A thermal switch assembly comprising a dielectric separator and a commutator sheet member compressively sandwiched between a pair of metal plates. Said separator has a surface notch therein that faces one of said metal plates. and said switch blade member has a mounting portion received in said notch, and said notch has a depth that is not greater than the thickness of said mounting portion.

31. The switch assembly according to claim 28 »further characterized in that said notch has a depth of at least about 90% of the thickness of said mounting potion.